Variable pitch propeller arrangement



Aug. 39, 1947.

A. G. FORSYTH VARIABLE PITCH PROPELLER ARRANGEIIENT Filed Nov. 14, 19427 Sheets-Sheet l Aug. 19, 1947. A. s. FORSYTH 2,426,007

VARIABLE 'PITCH PROPELLER ARRANGEIENT I Filed Nov. 14, 1942 7Sheets-Sheet 2 azdlbalai Aug. 19, 1947. A. e. FORSY TH VARIABLE PITCHPROPELLER ARRANGBIENT' Filed Nov. 14, 1942 Ill/ l'l'l'l'l 7Sheets-Sheet. 3

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9, 1,947. A. a. FORSYTH 2,426,007

' wmuansrrrca PROPELLER ARRANGE'IENT Filed Nov. 14', 1942 7 Shoots-Shoot4 Aug. 19, 1947. A. e. FORSY TH' v2,426,007

VARIABLE PITCH PROPELLER ARRANGEMENT Filed Nov. '14, 1942 7 Sheets-Sheet5 Aug. 19, 1947. A. e. FORSYTH 2,426,007

, VARIABLE PITCH PROPELLER ARRAHGEIEN'I' Filed Nov. 14, 1942 7Sheets-Sheet s r h T Q N 1 h arc/"bale! Gru/rarn MW,

Aug. 19, 1947. A. s. FORSYTH 2,426,007

VARIABLE PITCH PROPELLER ARRANGEMENT Filed Nov. 14, 1942 7 Sheet s-Sheet7 Patented Au 19, 1947' UNITED STATES PATENT orrlca VARIABLE PITCHPROPELLER ARRANGEMENT Archibald Graham Forsyth, Cheam, England, assignorto The Fairey Aviation Company "Limited, Hayes, England ApplicationNovember 14, 1942, Serial No. 465,618 1'Claim. (01. 170-163) Thisinvention relates to a variable pitch propeller system, and inparticular to a, variable pitch propeller system employing two sets ofpropellers for contra-rotation on coaxial shafts.

In my copending application, Serial No. 449,123, filed June 30, 1942, anarrangement of the general type is described in which the pitch of theblades of the propellers of each set may be changed to effect conditionsof fine pitch, coarse pitch, feathering and braking, the relativerelationship of the pitch of the blades of both sets of propellers,however, remaining the same at all times. In the above-mentionedapplication, means are illustrated and described for efi'ecting thedesired pitch at the will of the pilot as required v by flightconditions.

The present invention constitutes an improvement of such means, andprimarily resides in providing special means to efiect a more rapidadjustment from one pitch condition to another as emergency flight andlanding conditions may require.

Another object of the invention resides in the provision of boostermeans operable at the will of the pilot to assist the power means foreffecting a pitch change from one condition to another. The inventioncontemplates booster means of various types and includes both electricaland hydraulic instrumentalities adapted to accomplish the desiredresult.

Still a further object resides in an improved control for such boostermeans as related to the pitch changing system as a whole.

In accordance with the invention, the blades of the two propellers aremaintained in a. fixed relationship with respect to each other over theentire pitch changing range, the mechanism being so arranged that thepitch of the propellers may be the same or may differ to suit therequirements necessary to obtain maximum efficiency.

Further, in accordance with this modification,

position, and from coarse to feathering position. I

The invention effects pitch changing movement of the blades about theirlongitudinal axes through gearing arrangements such as described in mycopending application, such gearing being driven by a motor which may beelectric or hydraulic.

I tion.

booster motor to speed the pitch changing movement in either directionfrom reverse to flag posi- A further object resides in the provision ofcontrol means for actuating the booster means at the required periods.

These and other objects of this invention will become more apparent froma consideration of the following specification and claim when read inthe light of the accompanying drawings, in which: v

Figure l isa side elevation, partly in section, showing one form of theinvention;

Figure 2 is a cross-sectional view taken on line 22 of Figure 1; 1

Figure 3 is a view partly in elevation and partly in cross-section takenon the linev 3-3 of Figure 1; t

[Figure 4 shows a modification of the invention partly in cross-sectionand partly in elevation;

Figure 5 shows a still further modification in side elevation and partlyin cross-section;

Figure 6 shows in section a preferred form of a hydraulic systemadapted. to vary the propeller pitch;

Figure 7 is an end elevation on the line |'I of Figure 6;

Figure 8 is a cross-sectional view taken on the line 8-8 of Figure 6;

Figure 9 is a diagrammatic representation showing an electrical circuitarrangement used in carrying out this invention;

Figure 10 illustrates a modification of a hydraulic system adapted tovary the pitch of a propeller blade;

Figure 11 is a further modification of the arrangement shown in Figure10;

Figure 12 illustrates a modification of the booster motor arrangement;

Figure 13 illustrates a modified type of clutch adapted to be used inthis invention;

Figure 14 is a cross-sectional view taken on the line I4l4 of Figure 13.

In considering this specification and the accompanying drawings,attention is directed to my Patent No. 2,161,917 and my pendingapplication, Serial No. 449,123, filed June 30, 1942.

Referring now more specifically to Figures 1, 2 and 3 of the drawings,the reference numerals 2 and 4 indicate two propellers mountedrespectively on two coaxially disposed hollow drive shafts B and 8, eachor which are adapted to be rotatively driven by internal combustionengines (not shown) with each engine having its own In particular thepresent invention employs a '55 controls. Obviously, with such anarrangement it'bGOOlIlGS possible to operate the engines at any desired\speeds relative to each other, or to stop one engine while permittingthe other to operate.

In this embodiment of the invention, the roots of the propeller blades(in this case three on each shaft) are each mounted for rotary movementabout its longitudinal axis so that the pitch of the blade can beadjusted over a range of 360. To accomplish this movement, the root ofeach propeller blade 2, 4, is rigidly secured to ring gear it, which isengaged by a worm gear l2, l2 rigidly secured on the shaft l4, l4. Asthese gears are turned in one direction or the other by means to bedescribed, the worm gear l2, l2 will rotate the ring gears II) which,since the gears are rigidly mounted on the propeller blade roots, willrotate the blades about their respective longitudinal axes, thuschanging the pitch of the blades.

In the present invention the propeller pitch changing means for'theblades 2 comprises a reversible electric motor it which is provided witha drive shaft l8 on which is rigidly secured coaxially therewith thegearwheel 20 which coacts with the gear 22 (coaxial with respect to thepropeller drive shafts). As is clearly seen in Figure 1. t e gear 22 isprovided with a laterally extend-. ing flange portion 24 having gearteeth out on the outer periphery thereof. A spider 26 carries thecoaxially mounted gears 28 and 30, of which gear 28 is adapted to beengaged by the gear teeth formed on the flange 24 and to be rotatedthereby. A ring gear 32 has gear teeth formed on its inner peripherywhich are also engaged by the gear 28 mounted on the spider 26. A gear34 keyed to the frame 36 is adapted to mesh with the spider mounted gear28. The gear 28 also meshes with a second ring gear 38 which is rigidlysecured to the propeller hub. The ring gear 32 is provided with gearteeth cut on its exterior periphery which mesh with and rotate gear 40under certain conditions to be discussed below. The gear 40 is rigidlymounted on the shaft l4, which, it will be recalled, has also fixedlysecured thereon, the worm gear l2.

It is now seen that when the reversible electric motor 56 isenergized-to rotate in one direction, the gear 20, driven by the shaftl8, will rotate the gear 22 which in turn transmits its rotation throughthe gear 28 to the ring gear 32. The rotation of gear 32 will turn gear40 which, since it is mounted rigidly on shaft it, turns the worm gearl2. The worm gear 12 cooperates with the ring gear iii to rotate thepropeller blade 2 with respect to its longitudinal axis thereby changingthe pitch thereof.

The other end of the shaft i4 is provided with a second gear 42 fixedlymounted thereon. This gear, when rotated transmits power through agearing system identical to that previously described in order to varythe pitch of propeller blade 4. The various elements found in the secondgear train may be identified by-the primed reference numerals indicatingsimilar elements to be found in the first system.

One of the objects of this invention is to provide means whereby therate of change of pitch may be rapidly accomplished. This is achieved byselecting a high gear ratio with respect to gears 28 and 32. In additionthereto, it has been found advantageous to employ a booster motor 42 ofapproximately the same power as motor l6. Motor 42 is employed when itis desired to change the pitch from fine to breaking (and the reversethereof), and its cooperation with the gearing system is readilyunderstood.

The gear wheel 22 engages the freely rotating gear 44 rigidly mounted onone end of a shaft 40.

The other end of the shaft carries the female portion or clutch plate 48also rigidly secured thereon. The male portion 50 of the clutch istelescopically mounted on and is keyed to the drive shaft 52 ofthe'electric motor 42. A pivoted link 54 is secured at one of its endsto the telescoping member 50. The other end of the link is secured tothe shaft 56 which is operable by the energization of the electricsolenoid'58. The solenoid 58 and the motor 42 are controlled through anelectric circuit to be described.

In Figure 5. amodiflcation of the invention is illustrated. In thisfigurethe inner gearing system adapted to vary the'pitch of thepropeller blade 2 is identical to the gearing systems described inconnection with Figure 1, and identical reference numerals are employedto identify the same elements. However, in this modification, the gearwheel 42 engages the ring gear 50 which is provided with gear teeth onits outer periphery for this purpose. The inner periphery of the ringgear 60 is provided with gear teeth which are engaged by a gear 62mounted coaxially with gear 64 on the spider 66. The gear 64 meshes withgear teeth formed on the inner periphery of the ring gear 68 and alsocooperates with the gear 10 which is keyed to the shaft 8. As is seen inthe drawing, the gear 62 also meshes with the gear 12 which issubstantially U-shaped in cross section. This gear engages the gear 45which when rotated, will turn the worm gear l2, thereby varying thepitch of the propeller blade 4.

In Figure 4, another embodiment of the invention is illustrated. In thismodification the shaft l8 drives the gear 22. The gear 22 is engaged by.gear 28 mounted coaxially with gear 30 and is carried by the spider 26.The gear 28 engages teeth formed on the inner periphery of the ring gear14 which is rigidly secured to the propeller hub. The inner ring gear 16is provided with radially inwardly extending gear teeth which engagegear 30.

Gear 30 cooperates with gear I8 which is keyed to the frame 36. It willalso be seen that the gear I6 cooperates with the gear 80 which isrigidly secured to the shaft 14. Hence, it is easily seen thatenergization of the motor [6 will turn gear 80 which rotates thepropeller blade in the man- I ner described above.

The variable pitch gear mechanism is controlled through the equipmentand electrical circuit diagrammatically shown in Figure 9. Inconsidering this figure it will be seen that a portion thereof is quitesimilar to the electrical circuit shown and described in my copendingapplication, Serial Number 449,123.

Included in the circuit shown is a battery 200 for supplying current tothe electric motors I6 and 42, solenoid switches 202, 204, 206, and 208,manually operated featherin switch 2 I 0, a double switch 2I2, 2l2'operated by the governor 2l4 which is geared to a shaft 2l5 driven bythe internal combustion engine, a manually operated switch 2 l6 foroverriding the governor at the will of the operator, a braking switch M8and a series of limit switches 220, 222, 224, 226, 22'! and 228.

The limit switches are controlled by a number of cam shaped disks 220',222', 224', 226', 221' and 228' adjustably mounted on the shaft 230which is connected with the motor l6 through reduction governor isindicated in dot and dash lines. The fine pitch switch 222 and thecoarse pitch switch 224 are both located in the normal circuit. The

cams 222' and 224' are so positioned on the shaft 230 soas to permit theswitches 222 and 224 to be held in their closed position during normaloperation. In normal operation of this circuit the tension of the spring230 is adjusted to regulate the governor 2I4 to suit the R. P. M. of theengine decided upon by the pilot for operation. The governor whenoperating thus actuates the pivoted switch lever 232 so that it willeither close the fine pitch switch 2 I 2 or the coarse pitch switch2I2'. In accordance with the particular switch actuated the electricmotor ;I6 'will rotate the shaft 230-so as to tend to bringthe cams222', 224' into contact with their respective switch arms. If the camsare rotated far enough one or the other of the cams 222', 224 willactuate either the fine pitch limit switch 222 or the coarse pitch limitswitch 224, thus breaking the normal circuit and cutting off the motor.

The fine pitch limit switch 222 and the coarse pitch limit switchcontrol the predetermined coarse and fine positions of the propellerblade pitch, For example, the fine pitch limit switch acts to preventover pitching in a dive. In normal flight neither switch is actuated bytheir respective cams.

In this arrangement when the engine is stopped the governor weights 234move in such a manner as to close the fine switch 2I2 (the coarse switch2I2 can only be closed when the engine is operating). Thus the electricmotor I6 is placed under operation and will rotate the cam shaft 230until the cam 222' operates the switch 222 thereby breaking the motorcircuit. This insures that the blades will always be left in fine pitchfor a take oil.

Should it become necessary for any reason to over-ride" the. governor,the pilot may accomplish this by manually actuating the hand contr'olswitch 2I6 which is in the circuit indicated by clot and dash lines.Consequently, if this switch be actuated to cut out the governor, theelectric motor I6 will be actuated to rotate -'the cam shaft 230 so asto tend to cause the cams 222' or 224 to operate their respectiveswitches. The circuit to the motor is, of course, broken either byoperating the hand control 2 I 6 or by the opening of either of the twoswitches 222, 224,

When it is desired to feather the propellers, it is necessary for thepilot to actuate the feathering switch 2l0 so that the normal circuit(full line) is broken and the feathering circuit indicated in dottedlines, is made. As is seen, during normal operation no current passesthrough this circuit.

Operation of the feathering switch to close the feathering circuitpermits current to pass through the contacts of the feathering limitswitch 226 and at the same time since the normal circuit is dead, thecoarse pitch limit switch 224 will be dead so that actuation of thisswitch by the cam 224' will not operate to shut off the current to themotor I6. As the shaft 230' continues to re. tate, the cam 226' willoperate the feathering limit pitch switch 226 thereby opening thefeathering circuit, stopping the electric motor I6 and holding thepropeller blades in feathered position.

When the feathering limit switch 226 is broken, the fine pitch limitswitch 222 circuit is still alive, and due to the fact that the governorhas moved the pivoted switch into fine position; the electric ill motorI 6 is reversed and automatically rotates the shaft 230 to bring thecams 222' and 224'- back into position to actuate their respective limit,switches 22.2, 224.

It is also obvious that actuation of the hand control switch 2I6 in thehand control circuit' (broken line) may be used to bring the propellerblades back to normal position. It is necessary,

. ing switch2l0 is put into feathering position. 20

Moving the switch 2| 6 in a counter-clockwise direction from theposition shown to the first set of terminals will cut out the governorand com.- plete the fine pitch circuit. Moving it clockwise to the firstset of terminals will close the coarse pitch circuit. Continuing in thesame direction to a position at right angles to the first position willeffect an "off position in which the blades are locked. This switchobviously may be rotated as much as 360 in either direction. It will beapparent that usually this switch 2 I 6 will remain in a normal runningposition in which the governor is in actuation, but can be used, forexample, on long cruises and the like, so that the pilot can set thepitch in the best possible position for the most economical operation.

As was stated above, one of the objects of this invention was to providemeans for changing the pitch of the propeller blades rapidly from thefine pitcl'i position to breaking pitch position and reverse. Toaccomplish this feature of the invention, the booster motor 42 isbrought into operation and simultaneously one or the other of theelectric solenoids 266, 268 is energized to bring the clutch intoengagement to add the power of the motor 42 to that of motor I6. r

The braking limit switch 2) during normal operation is dead since thenormal circuit bridges it, but when it is desired to efiect the brakingposition after the aircraft is on th ground, it may be rendered live bybraking switch 2I8 interconnected with the brake pedal or lever (not oneside of the normally open switch240, the

other side of which is connected to the ground. The switch 240 isadapted to be closed by operation of a pin 242 when the latter is raisedby the pivoted arm 232 controlled by the governor 2.

In the normal position of switch 2 I 8, the switch connects a pair ofterminals, one of which 244 leads to the coarse" switch M2 and the other246 to the fine switch 2I2. This latter terminal 246 is also connectedin the hand control circuit by line 248 so that when'switch 2I8 is innormal position, the hand control switch 2I6 may still be actuated tooverride the governor.

In practice, the braking switch 2I8 is adapted to be operated by thefoot brake pedal when the plane lands. As the pilot applies the brakesthe switch 2I8 is turned from the position shown to its other position.This takes the current directly 7 to the braking limit switch 220,through the sole.

- 288 is energized simultaneously therewith and the armature thereofoperates to close the motor switch 250 thereby energizing the motor i2and also operates the linkage system to close-the clutch thereby addingthe power of the motor 42 to that of the motor I6. Motors I6 and 42 con.tinue to operate until limit switches 228 and 228 are opened by therotation of the cams 220 and Turning the hand switch 2!! to coarseposition and releasing the brake pedal the switch 2I8 is moved'back toits normal position and establishes an electrical circuit throughsolenoids 202 and 206 which reverses the direction of the rotation ofthe motors, and maintains the clutch in engagement with the motor 42.The shaft 23o continues to rotate until the switch 221. operated by thecam 22'! is opened simultaneously with the opening of limit switch 224,thereby opening the circuits through all motors and sole- 1101118. Thecams 221' and 228' normally hold the switches 221 and 228 in openposition, allowing them to become active only during the-brakingoperation,

In off" position switch 2I8 completes the negative for the coarse pitchcircuit (either governor or hand controlled) thereby making it-possibleto go into reverse pitch when reverse pitch is required (when plane ison the ground and a foot pedal braking is applied to place switch 2I8 in.on position) even when the pilot controls are in coarse pitch position.Inner terminals 236 and 288 complete th ignition switch wires andcomplete the circuit through the governor actuated switch 240 to groundwhen switch 2 I8 is in on position. Switch 240 is normally open and canonly be actuated to close the circuit when switch 2I8 is on. The switch240 is designed to break only when going into a revers pitch positionand only when a predetermined lower limit of R. P. M. is reached.

This arrangement constitutes a safety measure 7 since braking a reversepitch position of the propeller cannot be effected until the aircraft ison the ground and the pilot has applied the foot pedal and the motor hasslowed down to a predetermined R. RM.

Hence, it is seen that a rapid change from fine pitch to reverse pitchand the reverse is effected through the introduction of the powerderived from motor 42.

In Figure 6 a hydraulic system adapted to vary the pitch of thepropellers through the gearing arrangement described above isillustrated.

This embodiment employs a cylinder 82 which is provided with coaxialthreaded apertures 84 in the respective ends thereof. A piston 86 isrigidly and coaxially mounted on the shaft 88 which is in turn mountedin the apertures 84 to permit reciprocal movement of the piston 86 inthe cylinder 82. Threaded sealing rings 90 engage the threaded aperturesand are adapted to hold packing 92 securely in place. A gear rack 94 isrigidly secured to the ends of the shaft 88 by means 01'' the supports95. Adjacent each end of the cylinder 82 two openings 96 and- 98,respectively, are provided. One end of each of the pipes I and I02 isfixedly mounted therein and each end is packed (not shown) againstleakage. A suitable reversible hydraulic pump I02 is connected to theother ends. Consequently, operation of the hydraulic pump I02 in one dil8, rection will furnish fluid through one of the conduits I00, I02 andwill provide a suction on the other; reversing the pump will reverse thefunction of the conduit pipes. Pump I02 may be It controlled in any wellknown manner such as manually or by a governor operating in response mherotational speed of the engine and pro- It is to be understood thatfluid entering one 10 end of the cylinder 82 under pressure will forcethe piston 86 toward theopposite end and vice versa. In moving from oneend of the cylinder to the other, the fluid pressure acting on thepiston 86 causes a longitudinal movement of the gear rack 94. As is seenin Figures 6, 7 and 8,

the upper surface I04 01' the gear rack is substantially planar andcooperates with a similar surface on the bottom or base of the cylinder82. These cooperating surfaces prevent any rotation of the rack aboutthe shaft 88.

The' rack 94 engages the gear wheel 22 and as the fluid under pressureis admitted alternately to one or the other surfaces of the piston 86,the gear 22 is rotated first in one direction '26 and then the otherwhich results in achange of the propeller blade pitch as explainedabove.

In the event a more rapid change of pitch is required, a booster pumpand circuit is provided, the control thereof being positioned in thecockpit or is adapted to be operated by the brake pedal. The boostercircuit comprises a hydraulic pump I06 connected to a source of fluidsupply a (not shown) and is connected to the interior of the cylinderthrough conduits I08, I08. The

high pressure side of the conduit is, at the will of the operator,alternately connected with the interior of the cylinder at opposite endsthereof by adjusting valve II4. Whichever of conduits I08, I08'- is notconnected to the high pressure side of pump I06 is connected to thefluid when it is in closed position. This circuit comprises the pipe II0 and the spring tensioned valve device II2.

It .will be noted that the booster arrangement just described operatescompletely independently 01' the pitch varying arrangement whichincludes -conduits l00, I02. This has the advantage of not onlypermitting accelerated pitch changing movemerit of the blades whendesired, but also provides a safety factor in that a defect or breakagein one of the hydraulic fluid supply systems will not leave the pilotwithout means for changing the propeller pitch. In systems whereinbooster arrangements operate through one or more common parts, such as avalve, with the ordinary pitch control arrangement, a defect in thecommon part would disable both control systems.

Figure 10 illustrates a modification of the hydraulic system which maybe employed in effecting the rapid change of pitch, from fine to braking55 and the reverse thereof. This figure also shows a method for changingthe pitch of the propeller blades through their normal phases offine-pitch, coarse pitch and feathering.

In this construction, the cylinder 82', piston (not shown), gear rack94, supports 95', threaded apertures 84' and threaded sealing rings 90'are identical to the correspondin elements shown in Figures 6, 7 and 8.This embodiment employs but two conduits 300 and 302, one end of each ofthe conduits communicating with the interior of the 9 cylinder 82' at apoint adjacent each of its ends. The other ends of the conduits areconnected with a valve device 384 which is controlled by the governor386 connected to the internal combustion engine. I

A shaft 388 is mounted for reciprocal movement within the cylinder M8,the degree of movement being dependent upon the speed of the engine.Rigidly secured on the shaft 388 are the valve pistons 3|2,3i2'.

The intake port of the hydraulic pump 3l4 is connected to a source(container) of fluid supply 3l6 through conduit 3l8. The high pressureside of the pump 3 I4 is connected with a chamber 328 through pipe 322.The chamber in turn is connected with the interior of the valve 384through the conduit 322.

The container 3I6 is also connected to the cylinder 3| 8 adjacent eachend thereof by discharge conduits 324 and 326.

During normal operation of the internal combustion engine, the governorwill reciprocate the shaft 388 and, of course, the valvepistons 312,3l2', thereby connecting the conduits 388 and 382 with either the highpressure pipe 322 or with one of the discharge pipes 324 or 326. Thechange in pressure on one side or the other of the piston in thecylinder 82' will produce a movement of the gear rack 94 which istransmitted to the gear wheel 22 which rotates the propeller blades toeffect a change of pitch. r

In the event it is desired to-move from normal running pitch to brakingpitch, a booster pump 328 is provided. Pump 328 is energized by closingswitch 338 which may be connected with the brake pedal. The low pressureside of the p mp 328 is connected by. pipe 332 to the fluid suppl andthe high pressure side is connected with the chamber 328 through pipe334. A one-way valve 336 is introduced in conduit 334 intermediate thesupply through pipe 346, as shown when, how

sure on one or the other sides of the piston in I the cylinder-82' andwill efiect a more rapid change in pitch in the manner described above.

When braking pitch is no longer required, the

switch 338' and valve 348 are returned to their original positionsthereby cutting off the booster pump motor and connecting the lowpressure side of pump 3 M with only the fluid supply.

Figure 12 illustrates a modification of the arrangement of the normalpitch changing motor 48 and booster motor 42. In this illustration thebooster motor 42 is adapted to transmit its power (when required)directly to the shaft II when the motor 42 is energized and the clutchelements 48 and 58 are brought into engagement in the manner described.It will be seen in this figure'that the driving shafts of each motor arecoaxial and oppositely disposed.

chamber 328 and the pump 328 to prevent the higher speed. This will, ofcourse, change the pitch of the propeller blades very quickly. Apressure by-pass circuit comprising the valve 338 and the conduits 348,342 is also provided, the function of which is well understood.

In Figure 11 a still further modification of th hydraulic system isillustrated. In this system, the gear 22, cylinder 82', gear rack 94',conduits 388' and 382', discharge pipes 324 and 326, pumps 314' and328', valve device 384' and the governor 386' are identical'inconstruction to similar elements shown in Figure 10. In this embodiment,however, the high pressure side of the pump 3|4' is connected directlywith the governor operated valve device 384' through conduit 344. Thelow pressure side of the pump is connected to the fluid supply throughpipe 348, the three-way valve 348 and the pipe 358. The booster pump328' is connected at its high pressure side, with the valve 348 by thepipe 352, and the low pressure side is connected with the fluid supplythrough conduit 358'. (A bypassing circuit is also provided for thebooster pump 328 comprising the valve 338' and conduits 348', 342'.)

During normal operation only the pump 3l4' is employed to adjust the.pitch of the propeller blades. In this case the valve 348 is connecteddirectly with the valve device 384', and the fluid Figure 13 illustratesa modification of the clutching mechanism for the booster motor, In thisfigure, the motor 42 is energized and simultaneously therewith theelectro-magnets 488 mounted on the drive shaft 18 are also energized tocause the clutch plate 482 to engage the female clutch'portion 484 whichis rigidly secured to the drive shaft l8. 7

Having described my invention in detail, it is to be understood that theinvention is not to be limited to the specific examples described andillustrated herein, but is only limited by the scope of the followingclaim:

I claim:

In an airplane propeller pitch changing mechanism, a hydraulic cylinder;a piston in said cylinder; a rack and pinion arrangement drivablyconnecting said piston with the propeller blades; a first pitch controlarrangement comprising a reversiblehydraulic pump connected to supplyfluid under pressure selectively to either side of said piston; and abooster pitch control operable simultaneously with said first pitchcontrol 'for causing accelerated pitch changing movement of of fluid tosaid cylinder by thepump of-said first pitch control arrangement.ARCI-IIBALD GRAHAM FORSYTH.

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UNITED STATES PATENTS Date Number Name 2,236,841 Waseige Apr. 1, 19412,280,714 Martin Apr. 21, 1942 2,293,912 Mullen Aug. 25, 1942 2,246,745Martin et a1 June 24, 1941 2,333,973 Beebe Nov. 9, 1943 (Otherreferences on following page) Number 2,132,481 2,318,929

Name Date Number Country Date Kin Oct. 11;--1938 50,162 France Oct. 10,1939 Hoover May 11, 1943 464,203 Great Britain Apr. '12, 1937Schwarzhaupt et a1. Feb.-9, 1943 483,760 Great Britain Apr. 28, 1938Algarsson Mar. 16, 1943 5, 463,737 Great Britain Apr. 6, 1937 Beebe an.4, 1944 OTHER REFERENCES FOREIGN PAW The Bee-Hive, May 1938, pages 3 to6inc1u- Country Date sive, published by the United Aircraft Corp. GreatBritain Jan. 25, 1939 10 (CopyinDivision 9.)

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